Baby Soap False Positives on Drug Tests : Oops

Dish soap has been used to thwart drug tests, and now baby soaps have been shown to cause false positive THC (cannabinol) drug tests in hospital clinics. The common immunoassay used to screen for marijuana may have caused some very serious consequences.

Authorities have been using easy and relatively low cost drug screening tests to screen candidates (job candidates, parents of newborn babies, etc), judging individuals for “fitness” based on the results. But the tests are no good. And no one knew. Until now.

The test is the THC immunoassay. Now we know this test can indicate positive for marijuana in the presence of residue from common baby soaps. The issue is highlighted in a recent report in the Journal of Clinical Biochemistry entitled “Unexpected interference of baby wash products with a cannabinoid (THC) immunoassay“.

Staff at one clinical center had noticed an unusually high frequency of new babies testing positive for exposure to marijuana. They decided to investigate their testing methods. They started testing various baby products used in the lab to see if they could influence the results of the immunoassay drug screening test. One baby soap in the clinic caused positive tests for THC (marijuana).

Often the amount of soap needed to trick the test was very, very small:

The amounts of washes and soaps used within these studies were quite small, less than 0.1mL, and easily represent the amounts that could remain on the skin after use.

- Cotten, Duncan et al.

When the clinicians expanded the testing to other baby products, they found that numerous common baby products were able to cause (false) positive results on the marijuana exposure test.

Four out of seven commercial baby soaps caused assay interference sufficient to yield a positive screen result. The other three caused positive interference...

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This is a serious issue, because these screening tests are used to judge the fitness of a parent for parenthood. False positives cause undue concern for the babies, who are thought to have been exposed to a drugs also commonly believed to be a gateway drug, and commonly used with other substances.Positive test results can also trigger calls to law enforcement, housing officers, probation officers, school administrators, bosses, and parents.

These researchers note that the screening is intended to be only an initial screen, and that the scientific recommendation is to follow up on positive results with a more robust (and reliable) blood test. They also note, however, that this is rarely done. Costs and convenience issues lead most clinical workers to rely only on the screening tests when making decisions.

Please help raise awareness of this issue, so more clinical staff hear of it :

Adding irony to injury, the researchers acknowledge that some drug users have been tainting their urine with dish soap in hopes of causing false NEGATIVEs on the same drug tests. It seems the surfactants in soaps can cause all sorts of weirdness with these untrustworthy screening tests.